1. Field of the Invention
This invention relates to dish antennas, eg. for receiving and/or transmitting signals from satellites or terrestrial microwave antennas, and in particular means for heating such antennas.
2. Introduction to the Invention
The use of dish antennas, particularly for receiving signals from satellites, is increasing rapidly. Dish antennas vary widely in size, but many have diameters of 1 to 7 meters; for example, 1.2 meter and 1.8 meter aperture antennas are most frequently used for signals in the 12-14 GHz band which is widely used for private networks transmitting data, voice and video communications. FCC Regulation 25.209 sets radiation pattern sidelobe envelope requirements for both transmit and receive antennas, and a major concern of antenna manufacturers and users is to ensure not only that antennas meet those requirements when first manufactured, but also that they do not become distorted subsequently, so that the requirements are no longer met. If ice or snow is present on a dish antenna, it frequently causes distortion of the shape of the antenna and/or attenuation of the signal; the larger the dish, the more serious the problems are likely to be. Much effort, therefore, has been devoted to methods of heating dish antennas to keep them free from ice and snow. Unfortunately, however, no method has been found which is technically satisfactory and economically acceptable; and if care is not taken, the heating can itself cause distortion of the antenna.